Electronic speed sensor



Nov. 8, 1966 D. B. HEASLIP 3,234,668

ELECTRONIC SPEED SENSOR Filed Oct. 28, 1965 INVENTOR. DONALD B. HEASLlPATTORNEY United States Patent Ofiice 3,284,568 Patented Nov. 8, 19663,284,668 ELECTRONIC SPEED SENSOR Donald B. Heaslip, Sauquoit, N.Y.,assignor to The Bendix Corporation, Utica, N .Y., a corporation ofDelaware Filed Oct. 28, 1963, Ser. No. 319,162 3 Claims. (Cl. 3175) Thisinvention relates to speed-responsive, electrical controls and moreparticularly concerns such a control which is initiated byelectro-magnetic means.

Some motors, such as air turbine starters, require a speed-sensingdevice for interrupting the supply of air to the motor at apredetermined speed which corresponds to the speed necessary forstarting an engine. In the past, mechanical-fiyweight, speed-sensmgdevices have been frequently used. Such devices depend upon mechanicalmovement against springs and involve the wearing of rotating parts whichnecessarily affect the accuracy and reliability. These rotatingmechanical speed-sensmg devices also are relatively bulky and expensive.It has been proposed to use electro-magnetic means for generating aspeed-responsive signal which is used to actuate a control device forthe motor to be regulated. In one such proposal, a resonant'reed relayis actuated by the electro-magnetic means which generates an A.C.signal. In some instances, several closures of the resonant reed relaycontacts were necessary in order to provide sufficient power foroperation of the relay coil. This functionlng sometimes resulted in adelay and improper operation and hence has disadvantages.

An object of the present invention is to provide an improved electricalspeed-sensing control which does not rely on a mechanical, speed-sensingdevice whereby a wearing of rotating mechanical parts is avoided andmore accurate and reliable speed-sensing is realized.

Another object is to provide an improved electrical speed-sensingcontrol which is inexpensive, compact, and more sensitive.

A further object is the provision of a speed-sensing control having aresonant reed relay and an electro-magnetic speed sensing device whereinmore rapid functioning of the resonant reed relay is achieved so that acontrol device for a motor is more precisely operated at a predeterminedspeed.

The realization of the above objects, along with the features andadvantages of the invention, will be apparent from the followingdescription and the accompanying drawing.

The drawing is a schematic showing of a DC. source, a main controlswitch for circuitry including an electromagnetic pickup, a resonantreed relay, a silicon controlled rectifier, and a double-throw controlrelay.

Referring to the drawing, a DC. source 11 is connected to a main controlswitch 13 having wire 15 connected to lead 17 of the resonant reed relay19. Resonant reed relay 19 has a first reed contact 21 with lead 17 anda second reed contact 23 having lead 25. The resonant reed relay 19 alsohas a power coil 27 for causing the two reed contacts 21 and 23 tovibrate at a natural frequency for the closing at the contact tipsthereof. The resonant relay coil 27 is connected to the energizing coil29 of the electro-magnetic pickup device 31. The magnetic pickup device31 will generate an A.C. signal when energized by exciter rotor 33,having projections 35 of magnetic material. Rotor 33 is rotated by anair turbine starter (not shown). At a predetermined speed and frequency,the generated A.C. signal will correspond to the natural frequencyrequired for closing the reed contacts 21 and 23, as is well known.

A wire 41 extends from the juncture of wire 15 and lead 17 to the anodelead 43 of the silicon controlled rectifier (SCR) 45. The cathode lead47 from SCR 45 is connected to double-throw relay 49 by means of wire 51while the gate lead 53 of SCR 45 is connected to lead 25 of resonantreed 23. The double-throw control relay 49 has an actuating coil 61which has a predetermined inductance and is grounded and a loadresistance 63 is connected in parallel with coil 61. The relay 49includes a first fixed contact 65 which is normally open (N/O), a centermoveable common contact 67, and a second fixed contact 69 which isnormally closed (N/C). The common switch contact 67 is connected by wire71 to wire 41 at a location between SCR 45 and the main control switch13. The lower or first fixed contact 65 is connected to the juncture ofthe coil 61, the resistance 63, and the wire 51. The upper fixed contact61 is connected by wire 73 to a load 75 which is grounded. Load 75 canbe a normally-closed, air supply, solenoid valve for the mentioned airturbine starter.

The SCR 45 is a high speed, sensitive gating silicon controlledrectifier, such as the 2N1595 made by the Texas Instruments Company,Dallas, Texas. The load resistor 63 (used in parallel with the coil 63of the relay 49) has a value which permits a holding current to flowimmediately through the SCR 45 when first gated in spite of theinductance of coil 63 whereby the SCR locks in immediately and operatesmore proficiently under inductive load.

In operation, the switch 13 is closed and then the solenoid of thenormally-closed air supply valve or the load 75 is energized, wherebyair is supplied to an air turbine starter (not shown) and thus causingtoothed rotor 33 to rotate. The toothed rotor 33 is part of the startergear box (not shown) or other similar device. As toothed rotor 33rotates, an A.C. signal is generated in the coil 29 of the magneticpickup 31. This power signal is fed to the coil 27 of a resonant reedrelay 19. Below starting speed, the resonant reed relay 19 will remainopen since the output from the magnetic pickup is below the requiredresonant frequency. When a predetermined speed of rotor 33 is reachedand the frequency of the generated signal is the same as the naturalfrequency of the reeds 21 and 23 of the resonant reed relay 19, thereeds 21 and 23 vibrate and contact each other. At the first closure ofthe contacts on the tips of the reeds 21 and 23, the silicon controlledrectifier 45 is gated and slightly thereafter, the actuating coil 61 ofthe relay 49 is energized, causing the relay switch to operate. As thecommon element 67 of the switch breaks from the second or N/C contact69, the load 75 is de-energized. As the common element 69 of the switchmakes with the first or N/O contact 67, an additional holding circuit tothe relay coil 61 is completed. Relay 49 will not be de-energized untilswitch 13 is opened. The resistance 63 offsets the inductive load fromcoil 61 so that SCR 45 operates better.

It is to be noted that the use of the self-holding, silicon controlledrectifier circuit allows the relay 49 to operate after the first closureof the reed relay contacts 21 and 23. Many closures of the reed relaycontacts to prov1de the energy necessary for a relay of the type shownto switch to holding position do not result. As mentioned, theinductance of the relay coil 61 does not delay immediate flow of theholding current for the SCR since the load resistor 63 permits flow ofthe required holding current. The coil 63 operates a few millisecondsafter the SCR is initially gated with the consequent self-holding byflow through resistor 63. The inductance would prevent a self-holdingcurrent during the brief current flow at the first closing of thecontact reeds.

It is to be understood that changes can be made in the disclosedembodiment of the invention by persons skilled in the art withoutdeparting from the invention as set forth in the following claims.

What is claimed is:

1. A control system for a mechanical source of power having anassociated primary source of electrical power connected to a loadcomprising:

electrical signal generating means generating a signal proportional tothe speed of a portion of the mechanical source of power;

a resonant reed relay having a plurality of contacts electromagneticallylinked to the electrical signal generating means;

a silicon controlled rectifier having an anode, a cathode and a gate,one of said resonant relay contacts connected to the anode of thesilicon controlled rectifier, another of said resonant relay contactsconnected to the gate lead of the silicon controlled rectifier;

a switch means having a first electrical connection between the cathodeof said silicon controlled rectifier and the primary source ofelectrical power and a second electrical connection for the load, theswitch means controllingthe electrical energization of the load; and

the anode of the silicon controlled rectifier having an electricalconnection for the primary source of electrical power.

2. The control system as claimed in claim 1 wherein:

the switch means having a movable contactor, a coil and a plurality ofcontacts;

4 the movable contactor having an electrical connection relative to theprimary source of electrical power; one of the plurality of switchcontacts having electrical connection to the load, another of thecontacts having an electrical connection to the switch coil. 3. Thecontrol system as claimed in claim 2 including further: resistive meansconnected in parallel with the switch coil.

References Cited by the Examiner UNITED STATES PATENTS 2,941,120 6/1960Harman et al 317--5 3,213,323 10/1965 Circle 317148.5X

OTHER REFERENCES Silicon Controlled Rectifier Manual, second edition(General Electric), Dec. 29, 1961, pages 89-90 relied on.

New Design Ideas From Solid State Products, Inc., Bulletin #6,Controlling Relays with Microsecond Pulses, June 29, 1961.

1955 AIEE-IRE Electronic Components Conference at Los Angeles,California, A New Transistor with Thyratron-Like Characteristics, byRichard F. Rutz and Arvid W. Berger, May 26, 1955.

MILTON O. HIRSHFIELD, Primary Examiner.

J. A. SILVERMAN, Assistant Examiner.

1. A CONTROL SYSTEM FOR A MECHANICAL SOURCE OF POWER HAVING ANASSOCIATED PRIMARY SOURCE OF ELECTRICAL A SIGNAL CONNECTED TO A LOADCOMPRISING: ELECTRICAL SIGNAL GENERATING MEANS GENERATING A SIGNALPROPORTIONAL TO THE SPEED OF A PORTION OF THE MECHANICAL SOURCE OFPOWER; A RESONANT REED RELAY HAVING A PLURALITY OF CONTACTSELECTROMAGNETICALLY LINKED TO THE ELECTRICAL SIGNAL GENERATING MEANS; ASILICON CONTROLLED RECTIFIER HAVING AN ANODE, A CATHODE AND A GATE, ONEOF SAID RESONANT RELAY CONTACTS CONNECTED TO THE ANODE OF THE SILICONCONTROLLED RECTIFIER, ANOTHER OF SAID RESONANT RELAY CONTACTS CONNECTEDTO THE GATE LEAD OF THE SILICON CONTROLLED RECTIFIER; A SWITCH MEANSHAVING A FIRST ELECTRICAL CONNECTION BETWEEN THE CATHODE OF SAID SILICONCONTROLLED RECTIFIER AND THE PRIMARY SOURCE OF ELECTRICAL POWER AND ASECOND ELECTRICAL CONNECTION FOR THE LOAD, THE SWITCH MEANS CONTROLLINGTHE ELECTRICAL ENERGIZATION OF THE LOAD; AND THE ANODE OF THE SILICONCONTROLLED RECIFIER HAVING AN ELECTRICAL CONNECTION FOR THE PRIMARYSOURCE OF ELECTRICAL POWER.